The present invention relates to a personal authentication technique utilizing iris images, and more particularly relates to a technique for increasing accuracy of iris authentication in various situations such as under external light such as sunlight, in the night, and the like.
In recent years, a personal authentication technique utilizing iris images has been started to be used for entrance/exit management in a restricted building, bank ATMs (Automated Teller Machines), PC login applications, and the like. The iris, which has a complicated pattern, provides a very small false acceptance rate, showing applicability to special purposes requiring higher security levels. Nevertheless, the size of the pupil varies depending on ambient brightness, accompanying variation in iris pattern to invite increase in false rejection rate in the case where a lighting condition is largely different between at the time of registration and at the time of authentication. How to absorb the difference in iris pattern between at the time of registration and at the time of authentication is one of keys to reduction to practice.
Patent Document 1 discloses a principal method of iris authentication for identifying an individual by comparing iris image information obtained at the time of authentication with stored iris image information. In this method, an eye is illuminated while controlling the intensity of an illumination so that the pupil reaches a predetermined diameter size, and then, iris images or features extracted from the iris images are compared.
In Patent Document 2, a plurality of iris images in which pupil diameters are made different by changing the intensity of an illumination are taken at the time of registration, and a plurality of features extracted from the respective taken iris images are registered. Then, a feature extracted from an iris image taken at the time of authentication is compared with the plurality of registration features.
In Patent Document 3, various variations (pupil diameter, distortion, partition error) are provided at the time of registration to generate multiple feature data, and some thereof are selected to be registered.    Patent Document 1: Japanese Patent Publication No. 5-84166B    Patent Document 2: Japanese Patent Application Laid Open Publication No. 2000-194855A    Patent Document 3: Japanese Patent Application Laid Open Publication No. 2001-167279A